5/06/2009 @ 5:30PM

Why You Should Be Getting More Sun

According to a new study, 77% of Americans have insufficient levels of vitamin D. That’s a potentially serious problem, given recent research showing a link between low vitamin D levels and both cardiovascular disease and cancer.

Otherwise known as the sunshine vitamin, D is created when the body absorbs the sun’s UV-B rays. A handful of foodstuffs, including cod liver oil, salmon, tuna fish and fortified cereals and milk, are rich in the nutrient. But even fortified cereal and milk provide just 10% to 25% of the necessary daily value per serving.

Supplements do work, but there’s an even simpler way to get all the vitamin D you need: Spend a little time catching some rays. Exposing arms and legs to the sun for just 10-15 minutes three times a week can do the trick. For light-skinned people living where sun is abundant, that formula applies. Those with darker skin or in light-starved climates may need more time or a few doses of cod liver oil.

Until recently, vitamin D was believed to have a primary purpose: supporting bone health and strength. New findings are changing that view.

The Latest Research

In March, Dr. Adit Ginde, an assistant professor of surgery at the University of Colorado Denver School of Medicine, published the latest study in a string of scientific articles examining the prevalence and role of vitamin D. The article, in the Archives of Internal Medicine, looked at data collected between 1988-1994 and 2001-2004 from the National Health and Nutrition Examination Survey (NHANES).

Ginde and his co-authors compared levels of 25-hydroxyvitamin D, the product created once the liver converts vitamin D, and discovered that more than three-quarters of the American population has insufficient levels. They attributed the startling finding to the public’s heightened awareness of the dangers of sun exposure. Using sunscreen with an SPF of 15 decreases the synthesis of vitamin D by 99%. Another cause, they say, is less time spent outdoors.

Ginde’s study followed recent findings associating low levels of the vitamin with cardiovascular disease and cancer, and a February Archives of Internal Medicine article published by Ginde that established a link between low vitamin D levels and increased susceptibility to the common cold. Ginde and other researchers believe that vitamin D receptors in cells and tissue may help regulate the immune system.

“It’s very exciting and we think it’s likely a causal relationship,” says Ginde. But he also cautions that large-scale, randomized clinical trials are needed to prove the link.

How Much Vitamin D is Enough?

Dr. Michael Holick, a vitamin D expert at Boston University School of Medicine, has spent years advocating for increased vitamin D levels based on evidence that it plays a powerful role in maintaining the immune system. (The university has received $150,000 from the UV Foundation, an educational organization, to support Holick’s research on vitamin D.)

The Institute of Medicine, which is currently reviewing its guidelines, recommends varying levels of vitamin D depending on age: 200 international units daily from birth to age 50; 400 IU/d for adults between 51 and 70; and 600 IU/d for adults 71 and older. Holick’s recommendation of 1,000 IU/d, with an upper limit of 10,000, far exceeds the IOM’s guidelines. Research has yet to show toxicity for vitamin D.

For those who take the sunbather’s route to greater vitamin D consumption, some experts warn of an increased skin cancer risk. Marjorie McCullough, strategic director of nutritional epidemiology for the American Cancer Society, advises caution. “People shouldn’t look to the sun as their primary source of vitamin D,” she says. Instead, they should depend on a combination of limited sun exposure, diet and supplements.

Dr. Ginde is also careful not to overstate vitamin D’s potential, despite promising research and anecdotal stories.

“There’s reason to be optimistic,” he says, “but we shouldn’t be fanatics about it.”